There is a below-described patent document 1 which was previously filed by the applicant, as a valve timing control device configured to control to convert a relative rotational phase of a cam shaft with respect to a sprocket by using a rotational force of an electric motor.
This valve timing control device includes an electric motor including a motor housing configured to synchronously rotate with a crank shaft, and a speed reduction mechanism configured to reduce a speed of the rotation of the electric motor, and to transmit this speed-reduced rotation.
This speed reduction mechanism includes an eccentric shaft portion to which the rotational force is transmitted from the motor output shaft; an internal teeth constituting section including an internal teeth which has a waveform shape, and which is formed on an inner circumference; a plurality of rollers each of which are disposed between one of the internal teeth of the internal teeth constituting section and an outer wheel of a ball bearing; a holding device which is provided on a cam shaft's side, which separates the rollers within the plurality of holding holes, and which is arranged to allow a radial movement of the entire rollers.
There are previously prepared a plurality of rollers having different outside diameters. One of the rollers is selectively assembled in accordance with a size of a clearance (radial clearance) which is a backlash gap between the outer circumference surface of the roller and the inner surface of the internal teeth to adjust the backlash. With this, the generation of the hitting noise (tapping noise, hammering noise) by the rollers and the internal teeth during the operation is suppressed.